Probing electron-phonon and phonon-phonon coupling in type-II Dirac semi-metal NiTe 2 via temperature-dependent Raman spectroscopy.

We report the temperature-dependent structural characterization of type-II Dirac semimetal (DSM) NiTe₂ in the form of a bulk single crystal and a nanoflake (200 nm thick). Detailed x-ray diffraction study along with Rietveld refinement analysis reveals superior crystallinity and linear thermal expansion coefficient (αT) of 5.56×10-⁶ K-¹ and 22.5×10-⁶ K-¹ along a or b and c lattice directions, respectively. Temperature evolution of Raman spectra shows non-linear variations in the phonon frequency and full-width half maxima (FWHM) of the out-of-plane A 1g and in-plane E g modes. Raman mode E¹ 2g , corresponding to an in-plane vibration, disappears on decreasing the thickness from bulk to nanoflake. Quantitative analysis with anharmonic model yields dominating electron-phonon interaction over phonon-phonon interaction mediated by three and four-phonon processes.